Honing feed system having full control of feed force, rate, and position and method of operation of the same

ABSTRACT

The feed system ( 30 ) for a honing machine ( 10 ) provides a capability to dynamically correct in real time errors in bore size inferred arising from variations in feed force, and a method of operation of the same. The system ( 10 ) allows a user to select between rate and force controlled honing modes, which provides one or more of the advantages of both modes. The system provides capabilities for automatic rapid automatic bore wall detection, compensation for elasticity of elements of the feed system ( 30 ) and honing tool ( 14 ), and automatic tool protection. The system is automatically operable using feed force, feed rate and positional information for honing a work piece ( 20 ) to one or more target parameters, such as one or more in-process sizes and a final size.

This application claims the benefit of U.S. Provisional Application No.60/607,742, filed Sep. 7, 2004.

TECHNICAL FIELD

This invention relates to a feed system for a honing machine, and moreparticularly, to a feed system automatically operable using feed force,feed rate and positional information for honing a work piece to one ormore target parameters, such as one or more in-process sizes and a finalsize.

BACKGROUND ART

Traditional honing feed systems can be classified into two types: 1)Force controlled, and 2) Rate controlled. In a force controlled system,a constant or controlled force is applied to the feed rod/wedge of thehoning tool. The force can be applied by a spring, a cylinder, or othermeans. A measurement system or a mechanical trigger detects when thewedge has reached a point that is either known or inferred to be thefinished bore size. In a rate controlled feed system, a motor, typicallycontrolled by feedback from an encoder, moves the feed rod/wedge at aconstant or controlled rate. The bore size is inferred from the encodercount and can be calibrated or compensated for through an interactiveuser interface.

Each type of feed system has is own strengths and limitations. In aforce controlled feed system one advantage is speed. Fast, (nearlyinstantaneous) expansion of honing stones to the point of contact withthe workpiece bore and similarly fast retraction at the end of thehoning cycle are possible. In constant force systems, the wedge and feedsystem elasticity does not affect final bore size. There is no toolbreakage or excessive abrasive wear due to excessive feed forces. And,workpieces with less stock to be removed will be honed faster, i.e. notime is wasted while the honing stones expand at a relatively slow rate(selected for cutting) through the entire range of the maximumanticipated stock removal. Disadvantages include that cycle time cannotbe controlled, i.e. stones that glaze will hone with increasingly longercycle times. And, abrasives make rapid contact with rough or out ofround bores causing tool or fixture damage and/or wearing abrasivestones excessively.

Advantages of a rate controlled feed system include electronic controlof size, and electronic display of feed position during cycle without aseparate measuring system. And, honing cycle time will be consistent andunaffected by changes in abrasive condition. Disadvantages include thatfeed rod force is unknown. Feed forces can reach levels that endangerthe tool, fixture, or operator. Variations in the pre-process bore sizewill result in either wasted time or dangerous crash conditions. Thehoning process must start with the honing tool at some initial size.This position must be set for some point slightly smaller than thesmallest anticipated pre-process bore size. Honing a workpiece with alarger initial bore size must therefore include some wasted“air-cutting” time. Any workpiece with an initial bore size that issmaller than the initial tool size will be impacted violently as theabrasive feeds into the bore with full force during the tool's rapidexpansion to the starting size. Such impact is likely to the damage toolor the workpiece. And, since the force in the feed rod/wedge is unknown,the elasticity of those elements as well as the elasticity of the entiresystem introduces an error when inferring bore size from encoderposition.

In all types of honing feed systems it is desirable that the feedposition (i.e. position of the abrasive stones) be known during thehoning process. If the honing system does not include some in-processbore measuring means, then knowing the feed position accurately isessential for determining when the desired final bore size has beenreached. Most honing machines use some type of encoder or other positiontransducer on the feed system to infer the feed position.

For each honing application, optimum performance (as determined by borequality and cost per bore) will require the honing tool to operatewithin some limits of feed force and feed rate. Furthermore it ispossible that the optimum values of those parameters may be different atdifferent stages in the honing cycle. It is not possible to exactlycontrol both feed force and feed rate. The many variables affectinghoning performance will cause one of these two parameters to vary anytime the other is controlled exactly. However, there are significantadvantages to a feed system that constantly monitors the uncontrolledparameter and then uses that information to adjust the controlledparameter, to change the method of control, or to more accuratelydetermine the position of the abrasive stones.

Some hybrid systems already exist, but they fall short of the fullcontrol of the proposed invention as described below:

Reference in this regard, U.S. Pat. No. 3,849,940 (Yoshino et al.,Honing Machine) which describes a feed system that contains both aconstant force and a constant rate system mechanically coupled in such away that the faster of the two systems will control the expansion of thehoning stones. However, if the constant rate system is in control, thenthere is no means to measure feed force or to correct bore errors causedby variances in feed force. Also, it is not possible to select theslower system when it is desirable to do so, e.g. to improve boregeometry at the end of the honing cycle.

U.S. Pat. No. 4,187,644 (Fitzpatrick, Dual Feed Apparatus for MultipleSpindle Honing Machine) describes a feed system where a cylinder(constant force system) expands stones to the point where they contactthe workpiece bore and then the feed control switches to a constant ratemechanism. However, this system includes no means to measure feed forceor to correct bore errors caused by variances in feed force. Also, it isnot possible to select the controlled force system other than for theinitial rapid expansion of the stones.

U.S. Pat. No. 4,397,658 (Vanderwal, Feed Control For Honing or LikeMachines) describes an oil damper device to provide a slower initialfeed rate or even a constant feed rate for the entire honing cycle.However, this includes no means to measure feed force or to correct boreerrors caused by variances in feed force.

U.S. Pat. No. 4,679,357 (Richter et al., Method and Apparatus forDisplacing a Honing Tool) describes a feed system where a low valuetorque limit is imposed on a feed motor control so that stones may feedinitially very fast up to the point of contact with the bore, andthereafter a higher torque limit is allowed for honing. The torque limitof the motor is roughly equivalent to a limit on feed force, althoughmechanical inefficiencies limit the accuracy of using of torque limitsas feed force limits. This system also does not include a means tomeasure feed force or to correct bore errors caused by variances in feedforce. There also appears to be no means to control the honing feed to adesired feed force apart from merely preventing the force from exceedingsome limit.

European Pat. No. 0081383 (Fox, Improvements Related to Honing) claims acontrol system that uses feedback from a means for monitoring feedposition and velocity and a means for monitoring feed force. However,the details of the patent describe only a hydraulic feed system with aposition encoder. In such a system, feed force is inferred bymeasurement of hydraulic pressure and subject to errors such as thatinduced from frictional forces between the hydraulic piston and itsbore. Although the patent refers to means for monitoring force andposition, the use of an electronic load cell to directly measure feedforce is not mentioned.

European Pat. No. EP 0 575 675 B1 (Grimm, et al, Method and Machine forFinishing a Bore in a Work Piece) uses a feed force measuring device butonly for the purpose of determining the target end point (final encoderposition) for the honing process by expanding the honing tool into asize-calibrated ring with a feed force equivalent to that measured onthe previously finished workpiece. In a limited way this compensates forerrors caused by the elasticity of the workpiece and the feed systemcomponents, but as the compensation is a static correction based onforce measurements in the previous workpiece, it describes no means todynamically correct for variations encountered with the workpiececurrently being honed. It relies on the assumption that every workpieceis virtually identical to the previous workpiece in regards to hardnessand the amount of material to be removed. However, in most applications,this assumption cannot be made reliably. Also, this method makes nosuggestion that honing feed force can be controlled throughout thehoning cycle.

In all of the above-referenced prior art patents there appears to be nomethod to dynamically correct in real time for errors in bore sizeinference that arise due to variations in the feed force. Also, none ofthe referenced prior art patents gives the honing machine user theability to choose between rate controlled mode and force controlled modeor to program a honing cycle to switch between the two modes in a mannerthat could optimize performance.

Accordingly, what is sought is a feed system for a honing machine whichprovides a capability to dynamically correct in real time errors in boresize inferred arising from variations in feed force, provides a user theability to choose between rate and force controlled honing modes, andwhich overcomes one or more of the disadvantages and shortcomings of theprior art systems set forth above.

SUMMARY OF THE INVENTION

What is disclosed is a feed system for a honing machine which provides acapability to dynamically correct in real time errors in bore sizeinferred arising from variations in feed force, and a method ofoperation of the same, which allows a user to select between rate andforce controlled honing modes, which provides one or more of theadvantages of both types of feed systems discussed above, and whichovercomes one or more of the disadvantages and shortcomings of thesystems set forth above. Such a feed system is anticipated to have wideapplication for many types of honing tools and improve productivity ofmany honing applications. The system also provides capabilities forautomatic rapid automatic bore wall detection, compensation forelasticity of elements of the feed system and honing tool, and automatictool protection.

According to a preferred aspect of the invention, a basic system wouldinclude a feed rod or other feed element that is pushed (or pulled) by alead screw or ball screw driven by a feed motor or other driver, with adevice for determining a position of the feed element, such as anencoder. A gear reducer, or other mechanism and/or control, may becoupled with the motor or other driver to achieve the torque, speed, andposition resolution required by the system specifications. At theinterface or joint between the feed rod and the screw (or nut) would bea load cell or some other means to directly measure the feed rod force.The motor could be controlled by feed rate or the motor could becontrolled using feedback from the load cell to hold a constant feedforce during honing. More sophisticated computer control could have thefeed system following a programmed profile of feed rates, feed forces ora combination of both.

In the feed rate control mode of the invention, the system isautomatically operable to keep the feed motor moving at a constant rateor controlling the rate to some programmed profile that is a function offeed position. In the force control mode, the system automatically keepsthe feed motor moving in a manner such that the feed force is heldconstant or follows some programmed profile that is a function of feedposition. The profiles could alternatively be determined as a functionof another parameter, such as spindle load.

The system of the invention also allows for these two basic modes to bemixed within a honing cycle, e.g. honing at a controlled rate until somecondition is met then honing at controlled force until the bore is atfinal size. Furthermore the system allows for a high degree offlexibility in feed control programming. Parameters such as feed rate,feed force, spindle torque or load, time, number of reciprocationstrokes, workpiece temperature, and others can be used in real-timecontrol logic that adapts the controlled feed parameter or even changesthe feed control method in a simple or complex programmed manner.

Examples of typical application situations that can be resolved by thesystem of the invention include workpieces that are very rough orout-of-round from the previous process. To resolve this problem, thesystem can automatically set an initial honing rate which is very slowto make initial bore contact as gentle as possible. When the bore hasbeen improved sufficiently that the danger of faster honing is past, asautomatically determined either by a slowing of feed rate or the passageof a certain amount of time, then the machine control can automaticallyincrease feed rate or switch to a force controlled feed mode.

Another problem that can be resolved or avoided is distortion ofworkpieces that have non-uniform cross sections. The system canautomatically operate to initially remove material at a relatively highfeed force or rate, and then, at some predetermined distance beforereaching final size, the force or rate can be automatically lowered to avalue that relaxes the workpiece distortion and allows for improved borecylindricity.

The feed rate or feed force can also be automatically reduced to a verylow value at the end of the cycle for just a brief period of time orjust a few strokes to improve the resulting surface finish beyond thenormal range of the abrasive grit size being used.

Also, the system can automatically adapt responsive to changes in thecondition of the honing elements such as when the honing stones becomeglazed. By automatically monitoring cycle time or feed rate, thiscondition can be detected and the system can make the decision toincrease or decrease feed force until the undesirable condition has beencorrected.

The system can also automatically detect when one or more abrasivestones have completely worn, by either an unusual increase in feed forceor a by an excessively long cycle time.

Still further, the automatic elasticity compensation capability of thesystem is useful when a substantially constant feed rate is desired, todetect and automatically compensate for deflections in the feed systemwhich produce variations in true feed rate at the abrasive stones. Avalue for elasticity of the system can be determined at any time duringthe honing process, to allow for compensation for gradual changes inelements of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of a honing machine including afeed system according to the invention;

FIG. 2 is a simplified schematic representation of elements of thehoning machine of FIG. 1;

FIG. 3 is a simplified schematic representation of elements of the feedsystem of the invention;

FIG. 4 is a simplified graphical representation of feed force versesencoder position for the feed system of the invention;

FIG. 5 is a diagrammatic representation showing steps of a method of theinvention for machine setup;

FIG. 5 a is a continuation of FIG. 5;

FIG. 6 is a diagrammatic representation showing steps of a method of theinvention for machine operation;

FIG. 6 a is a continuation of FIG. 6; and

FIG. 7 is a simplified schematic representation of a feed drive for thesystem of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein a preferred embodiment of a feedsystem and method of operation thereof is shown, in FIG. 1, arepresentative computer controlled honing machine 10 is shown includingaspects of the feed system according to the present invention. Honingmachine 10 generally includes a spindle carriage 12 which is movable ina reciprocating stroking action, denoted by arrow A, by a linear motionsystem such as a conventional motor driven cam linkage mechanism, or aball screw, roller screw, linear servomotor, rack and pinion, hydrauliccylinder, chain, or belt, under control of a process based maincontroller 38. Here, carriage 12 is shown supported for reciprocalstroking action in a vertical direction, but it should be understoodthat stroking in other directions is also contemplated under the presentinvention. Spindle carriage 12 includes a honing tool 14, which can beof conventional or new construction and operation, generally includingan elongate mandrel carrying one or more honing elements such asabrasive stones or sticks which can be moved radially outwardly andinwardly relative to the mandrel, and which abrade and hone a surface ofa work piece in which tool 14 is inserted, as tool 14 is rotated, asdenoted by arrow B. In a typical application, as spindle carriage 12 isreciprocally stroked upwardly and downwardly, as denoted by arrow A,honing tool 14 will rotate in one direction or the other, as denoted byarrow B, within a hole or bore in a workpiece, for providing a desiredsize, surface finish and/or shape to one or more surfaces defining thebore or hole.

Referring also to FIG. 2, a simplified schematic representation of onepossible stroking apparatus of honing machine 10 is shown. Here, tool 14is shown inserted into a bore 18 of a workpiece 20 held in a fixture 22of machine 10, for honing an internal surface 24 of workpiece 20defining bore 18. Honing tool 14 is supported by a rotatable spindle 26for rotation denoted by arrow C, and reciprocal movement denoted byarrow A as effected by a ball screw drive mechanism 16, for effectingdesired honing of surface 24 of workpiece 20. Spindle 26 is rotatablydriven by a drive 28 in the well known manner. Honing tool 14 isradially expanded and retracted by a feed drive 86, under control of afeed system 30 of the invention, as will be explained below. Spindle 26supporting tool 14, as well as drive 28 and elements of drive 86, aresupported on a spindle support 32 connected to a ball nut 34 of ballscrew 16, so as to be movable longitudinally along ball screw 16 aseffected by rotation of a servo motor 36 in connection therewith. Ballscrew 16 is precisely rotatable by servo motor 36, the number ofrotations of and the rotational position of which being preciselydetectable by an encoder or other sensor (not shown). Ball nut 34 ismoved longitudinally along ball screw 16 by the rotation thereof, andfrom the rotation count of ball screw 16 the longitudinal position ofball nut 34 is determined. Servo motor 36 is controllable by a processorbased main controller 38 for stroking spindle carriage 12 and honingtool 14, as desired or required for achieving a desired parameter orparameters. Here, it should be noted that it is further envisioned thatball screw 16 could be substituted with any other means of rotary tolinear motion conversion (e.g. rack & pinion), or that the motor,encoder and ball screw together could be substituted with a linear motorand linear encoder, or any other system of providing position controlledlinear motion.

Turning to feed system 30 of the invention, in FIG. 3, one possibleembodiment of a feed drive 86 is shown. A feed motor 40 of drive 86 isconnected to (or is integral with) an encoder 42. If needed to providethe desired characteristics of output torque, output speed, and lineartravel per encoder count, a gear reducer 44 may be attached to the shaftof the feed motor 40. The gear reducer output shaft is connected to aball screw assembly 46 by a coupling 48. The ball screw assembly 46resists axial motion by means of ball bearing 50 held in a feed systemhousing 52. (The feed system housing 52 may consist of several pieces asrequired for ease of manufacturing and assembly.) The ball screw engagesa ball nut 54 that is attached to a ball nut carrier 56. The ball nutcarrier 56 is prevented from rotating by a key 58 that engages a slot 60in the feed system housing 52. Rotation of the feed motor 40 andsubsequently the output shaft of the gear reducer 44 causes the ballscrew to rotate, which in turn imparts a linear motion to the ball nut54 and its carrier 56. The key 58, in this embodiment, is integral witha retainer 62 that has a pocket to hold a round disc 64. The round disc64 is attached to one threaded end of a load cell 66. The pocket has avery small amount of clearance with the round disc 64 for the purpose ofallowing the round disc 64 to align itself with the components belowwithout creating any undesirable stresses on the load cell 66. The loadcell 66 is fastened to a non-rotating feed rod 68, which is preventedfrom rotating by a key 70 which also engages the previously mentionedslot 60 in the feed system housing 52. The non-rotating feed rod 68 isattached to a tube holding an arrangement of angular contact bearings72. The rotating races of the bearings 72 are attached to a rotatingfeed rod 74. The rotating feed rod 74 is splined or keyed by some meansso that it will rotate with the honing machine spindle shaft 76 and yetallows relative axial motion between the spindle shaft 76 and the feedrod 74. The spindle shaft 76 holds the honing tool 14 which contains awedge 78 for expanding abrasive honing elements 80 into the bore of theworkpiece 20. The wedge 78 is attached to the feed rod 74 and is allowedto move axially with the feed rod 74 while the tool 14 is restrainedfrom axial movement by its connection to the spindle shaft 76. Thisrelative axial motion of wedge 78 and tool 14 creates theexpanding/retracting motion of the abrasive honing elements 80. The feedsystem housing 52 and the spindle shaft 76 are both connected tocarriage 12 (FIGS. 1 and 2) that strokes them together to generate theaxial reciprocation of the honing process.

The axial force of the wedge 78 to expand the honing elements 80 isdeveloped from the torque of the feed motor 40 and converted to a linearforce by the ball screw and nut and then transmitted through the loadcell 66 to the feed rod 74 and wedge 78. The load cell 66 thereforealways senses the full axial feed force of the honing process. The loadcell cable 82 is carried through a cable carrier to an amplifier 84 (ifrequired). Power to and signals from the load cell 66 run through thiscable 82 and amplifier 84 to a processor based feed control 146 and aservo controller 148 of feed drive 86, in connection with motor 40 andencoder 42 of drive 86. The control of these devices as described in themethods below result in signals that precisely control the motion of thefeed motor 40.

There are two basic methods of feed control. The first is feed ratecontrol, where the control system keeps the feed motor 40 moving at aconstant rate or controlling the rate to some programmed profile that isat least partially a function of feed position. The second basic methodof feed control is force control, where the control system keeps thefeed motor 40 moving in a manner such that the feed force is heldconstant or follows some programmed profile that is at least partially afunction of feed position.

Computer control also allows for these two basic methods to be mixedwithin a honing cycle, e.g. honing at a controlled rate until somecondition is met then honing at controlled force until the bore is atfinal size. Furthermore the computer control allows for a high degree offlexibility in feed control programming. Parameters such as feed rate,feed force, spindle torque, time, number of reciprocation strokes,workpiece temperature, and others can be used in real-time control logicthat adapts the controlled feed parameter or even changes the feedcontrol method in a simple or complex programmed manner. The followingexamples are typical application situations that can be resolved byprogramming in this manner.

Workpieces that are very rough or out-of-round from the previous processcan create dangerous impacts when honing feed is controlled by force oreven when the honing rate is set too high. An initial honing rate can beset very slow to make initial bore contact as gentle as possible. Whenthe bore cleans up sufficiently that the danger of faster honing ispast, as determined either by a slowing of feed rate or the passage of acertain amount of time, then the machine control can increase feed rateor switch to a force controlled feed mode.

Workpieces that have non-uniform cross sections tend to distort underhigh feed forces. Most of the material could be removed at a relativelyhigh feed force or rate and then at some predetermined distance beforereaching final size the force or rate can be lowered to a value thatrelaxes the workpiece distortion and allows for improved borecylindricity.

The feed rate or feed force can be reduced to a very low value at theend of the cycle for just a brief period of time or just a few strokesto improve the resulting surface finish beyond the normal range of theabrasive grit size being used. This sometimes allows for using coarsergrit for faster stock removal and yet still achieve surface finishrequirements.

During the honing process the surface of the abrasive stones can changein condition ranging from open and free cutting to glazed. By monitoringcycle time or feed rate, this condition can be detected and the controlsystem can make the decision to increase or decrease feed force untilthe undesirable condition has been corrected.

When one or more abrasive stones have completely worn, this system candetect that condition by either an unusual increase in feed force or aby an excessively long cycle time.

If a truly constant feed rate is desired, the control system cancompensation for deflections in the feed system which produce variationsin true feed rate at the abrasive stones. (See Elasticity Compensationbelow.)

In certain applications it may be advantageous to maintain a constant orprofiled level of spindle torque. This can be accomplished throughfeedback from the spindle drive to control the motion of the feed motor.In such an application the feed force is not controlled and may vary.The present invention will compensate for bore size errors due to systemelasticity.

As with other existing honing control systems, this system may includesuch features as automatic stone wear compensation, manual bore sizeadjustment and/or integration with an in-process or post process gage tocompensate for abrasive wear and to improve bore cylindricity.

In addition to these and many other useful control schemes, thecontinual real-time computer monitoring and control of feed force andfeed position, integrated with the honing machine control allows forthree new performance enhancing features: automatic bore wall detection,elasticity compensation and automatic tool protection.

Automatic Bore Wall Detection.

Prior to the beginning of the honing cycle the honing tool has beenretracted to a size that allows for easy entry into the bore. If thehoning cycle then starts with the feed motor moving at the honing feedrate it can take several seconds of “cutting air” before the abrasiveactually begins to contact the bore wall or surface. To minimize this,often the tool is rapidly expanded to a size just smaller than thesmallest expected workpiece bore before slowing down to the honing rate.However, pre-process bores typically vary considerably in size and thosethat are larger than the smallest expected bore will still have wastedtime as the honing tool moves slowly from that position to the point ofcontact. Also, if a pre-process bore is smaller than the smallestexpected bore, then the stone will be fed into the bore wall at a highrate of speed. The impact could damage either the tool or the abrasiveor the workpiece fixture.

Controlling the honing to a feed force can eliminate the wasted time,but if the retracted tool diameter is too much smaller than the boresize the feed system may have too much distance to accelerate the stonesunder no load and when they reach the bore wall they have sufficientvelocity to create an impact. Again, the impact could damage either thetool or the abrasive or the workpiece fixture.

The high speed impact of the stones with the bore wall is potentiallydamaging because the spindle is turning and the stones will immediatelygrip the workpiece on contact. If the spindle is not turning, thenhoning machines with no feed force measuring device have no way ofdetecting when the bore wall has been contacted. Therefore, in the pastit was a necessity to have the spindle turning when the feed system wasin the rapid feeding phase.

With the present invention, however, the spindle can remain off whilethe feed system moves at a high rate of speed. Contact with the borewall or surface is seen by an immediate rise in the measured feed force.At that point the feed position is retracted very slightly to justremove the pressure of stones against the bore wall and then the spindleis started and the honing cycle can begin with no time wasted “cuttingair”. The high speed of the feed motor and the fast response of thecontrol system allows for this step to happen in a very brief period oftime, much less than the time that would have been needed to have thestones safely approach the bore wall. Since the spindle is not turning,the impact can be done at high speed with no danger of damage to tool orworkpiece (except possibly when unusually delicate tools are involved).

An ancillary benefit of this method is that the control system is ableto determine or identify encoder information representative of the boresize at the moment of impact. If a bore is seen as already larger thanthe finished hone size then the control system can respond accordinglyto alert the operator or automatically remove the defective workpiecefrom the workflow.

Elasticity Compensation-Measurement and Feedback to Improve Size ControlPrecision.

If the feed force is not held at a constant value from one cycle to thenext, the difference in feed force results in different degrees ofdeflection of all the feed system components including the tool, wedge,and workpiece. This variance in system compression (or tension forpull-type tools) adds an error to the size control results when theencoder position is used as a means of knowing final bore size. Thiserror is most troublesome to rate controlled process when workpieceshave a wide variation in the amount of material that must be removed.

With a load cell used in conjunction with the encoder, this system willhave the ability to measure and compensate for the elasticity of theentire system. A value representative of the elasticity of the feedsystem components can be calculated from encoder and load cell readingstaken during an automatic initialization routine (described in detailbelow).

In the past when setting up a honing machine, the control system wasrequired to be “taught” the location of the feed system (including thetool, wedge, and stones) relative to the bore of the workpiece. Thisinitialization step is has always required the operator to work inconjunction with the machine control and a certain skill or “trainedfeel” has been required to perform this operation accurately. Theoperation has been called “size initialization” or “snugging” becausethe operator moves the feed system by a manual input until he feels theworkpiece is snug on the tool. The accuracy of this operation depends onthe operator's ability to feel when the workpiece is as snug on the toolas it will be when the finished size is reached in the honing cycle.

With this new feed system it is possible to use a new technique for sizeinitialization that eliminates the effect of operator skill and at thesame time gathers data that can be used to make the honing process moreprecise. The machine control will instruct the operator to move the feedsystem to a point where the workpiece is almost snug on the tool. Thenthe operator will press a button to have the machine control start theinitialization sequence. The sequence begins by the feed systemautomatically retracting by an amount sufficient to be assured that theabrasive stones are no longer contacting the bore. Then the feed systemwill automatically begin to expand at a rate that is similar to theexpected rate of honing. After moving a distance sufficient to take upany backlash in the system, the control system will automatically beginstoring data points of encoder position and feed force. These pointswill fall along a curve that has the general shape shown in FIG. 4.

Examining FIG. 4, the curve shown can be divided into two regions. Thefirst region, which is substantially flat, is the region of non-contact.In this region the abrasive stones have not yet been expanded to thepoint where they contact the bore wall. The force level measured in thisregion represents a baseline value of force. This baseline value is acomposite of several things. First, due to friction there will always besome drag on the feed system as it moves. Second, if the system isvertical, the weight of the feed system components will place a staticload on the measuring device. Lastly, the measuring device itself mayproduce some non-zero value at no load due to minor inaccuracies inmounting or due to variations in electronic characteristics of themeasuring device. This baseline force level is recorded so that it maybe subtracted from the force values in the second region of the curve todetermine the true force values as a function of encoder position.

In the second region of the curve the abrasive stones have made contactwith the bore wall and the feed force rises as the feed motor continuesto advance. This is the region of elastic contact. The curve is notperfectly linear in this range as elastic theory might suggest. This isdue to the fact that some components are in contact and the area oftheir contact regions is increasing with load (e.g. the balls and racesin the thrust bearings, and the imperfect abrasive stones against theimperfect bore wall).

The control system must decide when the feed system has reached theregion of contact. Due to some level of noise in the measurements, it isconvenient to define the beginning of the contact region as the pointwhere the force rises to some small but significant level over thebaseline force. In the figure, this level of force is termed F_(c) andthe corresponding encoder position x_(c). For convenience this point istaken as the origin of a new set of coordinates labeled X′ and F′ wherex′=x−x _(c)andF′=F−F _(c)Although the graph is drawn with the encoder position as the independentvariable, it will be more useful for control purposes to say that therelative encoder position is a function of feed force:X′=f(F′)Or perhaps a more appropriate way to describe this is that once theabrasive stones are making contact with the bore wall, the additionaldistance the encoder can be moved is a function of the force required tocompress (or extend) the feed system components to reach that position.

An approximate mathematical expression for this function can bedetermined by using the data points with any number of curve fittingtechniques. The resulting function may be linear, non-linear orpiece-wise linear. The simplest technique is to assume linearity and usetwo points to determine the line. This technique may often be sufficientsince the feed force during the honing cycle is usually with a smallrange. If the operating range of force is known or can be estimated fromexperience, then two points can be used at or near the ends of thatrange. On the graph, these points are shown as (x₁, F₁) and (x₂, F₂). Inthat case, the slope of the line is given byk=(F ₂ −F ₁)/(x ₂ −x ₁)where k is a spring constant in the classical sense quantifying theelasticity of the system.

Once expressed mathematically, the control system will be able to usethis function to automatically make bore size corrections to the encoderinferred bore size, based on the measured feed force in real time at anypoint in the honing cycle. To do this, since both the force value fromthe load cell and the encoder reading are relative values, it will benecessary to have some point of reference. This point of reference canbe any point on the contact region of the curve. On the graph it isshown as the point (x_(r), F_(r)) Then in general the functiondescribing the curve can be expressed asx−x _(r) =f(F−F _(r))

If linearity is assumed this becomesx−x _(r)=(F−F _(r))/kThe control system can then use this function during honing to moreaccurately know bore diameter at any point in time by this formula:D=D _(i) +[x−x _(r) −f(F−F _(r))]LR _(t) /NR _(g)If linearity is assumed this becomesD=D _(i) +[x−x _(r)−(F−F _(r))/k]LR _(t) /NR _(g)Where D=current bore diameter (mm)

-   -   D_(i)=the bore diameter of the initialization workpiece (mm)    -   x=the current encoder position (counts)    -   x_(r)=the reference encoder position (counts)    -   F=the current feed force measurement (N)    -   F_(r)=the reference feed force measurement (N)    -   f (F−F_(r))=the encoder correction function, as described above        (counts)    -   k=a linear encoder correction constant, as described above        (N/count)    -   L=lead of the ball screw (mm/ball screw rev)    -   N=encoder size (counts/motor rev)    -   R_(g)=gear ratio (motor rev/ball screw rev)    -   R_(t)=tool ratio (diameter movement/axial movement) where:    -   R_(t)=tanθ for single stone tools    -   R_(t)=2 tanθ for multi stone or sleeve tools    -   θ=wedge angle

In controlling the honing cycle, rather than knowing the current borediameter, it may be more important to identify a target encoder position(e.g. a position corresponding to final diameter or to the diameter atthe end of a certain honing stage). Since this target encoder positionwill change as feed force changes, the formulae above can be rewrittento give the desired target encoder position as follows:x _(t)=(D _(t) −D _(i))NR _(g) /LR _(t) +x _(r) +f(F−F _(r))If linearity is assumedx _(t)=(D _(t) −D _(i))NR _(g) /LR _(t) +x _(r)+(F−F _(r))/kwhere x_(t)=target (or final) encoder position (counts)

-   -   D_(t)=target (or final) diameter (mm)

The feed force level F, in general will not be the absolute measurementfrom the force measuring device. As mentioned previously, there existssome baseline or background level of force due to frictional drag, theweight of the feed system components and possibly from errors induced inthe measuring device due to imperfect alignment in mounting. Thesevalues tend to be relatively static, changing only slowly over time, ifat all. The force used in controlling the feed system as described abovemust be the differential amount of force, therefore it is important toquantify this baseline level of force so that it may be subtracted fromthe raw force measurement. One technique for measuring the baselinelevel of the force signal is to take a reading immediately at thebeginning of the cycle when the stones are known to not be yetcontacting the bore wall. This can be done on every cycle and therebycontinually compensate for any changes in the baseline signal level. Ifthe Bore Wall Detection routine described above is being employed, thissame technique can be used providing that the feed system has retractedat least enough to allow the time for reading the baseline signal beforethe stones contact the bore wall.

Using Tools that Require Significant Feed Force to Expand.

For simplicity in the descriptions above and in FIG. 4, it has beenassumed that baseline level of force is some relatively small constantvalue. However some honing tools require some non-zero and possibleincreasing force just to expand the abrasive portion of the tool (e.g.abrasive plated sleeve-type tools). In this case the baseline is not asimple constant value, but rather it is a curve of force versus encoderposition. With such tools a slight variation must be made to theautomatic rapid bore wall finding and the elasticity compensationtechniques described above. An added step is required at the beginningof these techniques.

This first step will consist of moving the feed system through theexpected range of motion at approximately the expected speed with thetool completely out of any workpiece bore. During this time the controlsystem reads force and encoder position to generate a baseline curve.This curve then represents the amount of force at the given encoderposition that must be subtracted from the total forces that are measuredduring the rapid bore wall finding or the elasticity measurementroutines. After subtracting the baseline curve from the total measuredcurve, the resultant curve will be identical in form to the curve shownin FIG. 4 and the mathematical treatment of this rectified data canproceed exactly as previously described.

If this baseline force curve is expected to vary slightly over time dueto bore size compensations or environmental factors, the baseline can bere-measured at any desired frequency.

Automatic Tool Protection.

At the initial start, or even during the honing operation, there is apotential for damaging the tool, and possibly the workpiece fixture,when the feed system is expanding the honing element at a high rate.Because the spindle is turning at the time that the honing element isbeing fed it is possible that the abrasives of the honing element willimmediately grip the workpiece on contact causing the tool to twist.This potential for damaging the tool also exists at setup during the“size initialization” or “snugging” operation. This action requires askilled operator to manually expand the honing element against thesurface of the bore of the workpiece to determine a reference for thebore diameter. It is possible that during this process the operatorcould damage the tool by over expanding and crushing the abrasives ofthe honing element against the surface of the bore.

Referring also to FIG. 7, with the present invention, feed drive 86includes a system that can detect an abnormally high force yet issensitive enough to react at once to protect the tool and workpiecefixture from damage. The feed system takes advantage of the load cell tomonitor the force during feed expansion and immediately retracts thehoning element when the feed force exceeds a predetermined stored limit.The new feed system monitors and automatically controls servo controller148 thereof to retract the honing element with minimal delay toeliminate the possibility of the tool seizing the workpiece.

The feed system control automatically prevents the operator frommanually expanding the tool any further if this feed force overload, orfault, condition existed during “size initialization”. In addition toautomatically retracting the honing element, the new feed system canalso independently notify the main controller 38 of the fault conditionthrough an I/O interface. The warning is given whether the fault tookplace during the “size initialization” or during a normal honingoperation. This notification in turn would allow main controller 38 tohalt other operations and inform the operator of the fault condition.

Feed System Control.

A typical main control system of a honing machine, such as controller 38of machine 10, typically has to share its processing power among thevarious tasks that it is to perform. The performance features describedabove would require the control system to run at very high speeds toinsure the sensitivity and response time required from them. This wouldlikely mean that the controller would have to process all the data inreal time to minimize delays and react immediately to changes in thefeed force. Besides monitoring the feed system, the processor would alsohave to split its processing time among the other tasks that itperforms. However, a more direct method of control is available if thetask of processing the feed system is given to the feed drive unit. Toobtain this prerequisite, linearity would have to be assumed and theunit would have to be capable of using an external signal as feedback.

The present invention utilizes such a control system. According to thisembodiment of the invention, tasks pertaining to the expansion andretraction of the honing element are performed by feed drive 86, alongwith monitoring and reacting to any stimuli, such as from the load cell.This method of controlling the feed system directly by means of the feeddrive 86 eliminates possible processing overloads in the main controller38, and provides quick response. It assures the most sensitive means tomonitor and respond to changes in the feed force by immediatelyretracting the honing element with minimal delay when the surface of thebore of a workpiece is found or a force overload condition exists.

Referring also to FIG. 7, the feed system control referred to in thisinvention manages all inputs and outputs to and from drive 86 along withthe load cell circuits. The load circuits consist of a transducerinterface circuit 150 and a signal conditioning circuit 152, anautomatic tool protection circuit 154, an automatic bore detectioncircuit 156, and the control 146 managing the feed force and feed ratefunctions.

One of the unique features of this invention is its ability to controlthe feed system at such a wide range of feed forces required bydifferent tools, yet be sensitive enough to distinguish small changes inthe feed force when determining when the honing element has contactedthe bore. This automatic force scaling is accomplished in the transducerinterface and signal conditioning circuits 150 and 152, and is based onthe expansion and retraction forces required by the specific tool used.

The Automatic Bore Detection (ABD) circuit 156 monitors the feed speed,force, and position while the tool rapidly expands in the workpiece.Upon reaching the surface of the bore the feed position and force areboth automatically captured and saved. This is followed by the feedsystem immediately retracting to release the abrasive pressure off ofthe workpiece. This triggers the main controller 38 of the honingmachine to begin moving the other axes. The actual honing process isthen started when the feed force and position that had been savedearlier are used to rapidly feed the honing element out to the boresurface while the tool is spinning and stroking.

The ABD circuit 156 employs a method of detection to compensate for anynormal feed force changes in the system that might occur over time.Among these types of changes is the frictional force along the tool'stravel that can vary as the abrasives wears over time. The location ofthe feed system along the tool's total travel is based on whatpercentage of the tool's total range is used and also on the amount ofnormal wear of the tool's abrasive during the honing operation. Anotherfactor to consider is the amount of drag due to friction on the feedsystem as it is moving.

Without compensation these forces can affect when the bore is detected.To compensate for changes like these, the ABD circuit 156 monitors thefeed force at the beginning of each cycle as the honing elementapproaches the workpiece to determine a baseline level of force, andthen automatically computes a minimum force that will indicate when thehoning element reaches the bore surface. (F_(c) in FIG. 4.)

As described previously (Elasticity Compensation), the sizeinitialization step becomes an automatic process rather a manual one.This step employs the automatic bore detection feature to eliminate theneed for operator feel.

The Feed Force & Rate Regulator of control 146 controls the feed motor40 based on the mode of the application. The application may require aconstant feed force or constant feed rate or any combination of the twoduring the honing process. Incorporating the feed force and rateregulator in the drive unit allows the switching between the two modesvirtually instantaneously and can be done at any time during the honingprocess.

In the constant force mode the regulator will control the feed motorrate of speed to maintain a specific feed force. A distinctcharacteristic of this invention is the ability of the regulator circuitto filter out any outside forces that may influence the actual feedforce that the system is trying to maintain.

Unlike other systems running at a constant rate, the feed systemdescribed in this invention will maintain a specific feed rateindependently of the generated feed force while continuouslycompensating for the elasticity of the entire feed system. In theconstant rate mode the automatic elasticity compensator circuitdynamically updates, in real time, the final position of the feedsystem. The final position update is based on the variance in systemcompression (or tension for pull-type tools or a combination of tensileload with torsion loading of rotary systems) the feed system experienceswhile expanding the tool and assures an accurate and repeatable finishedsize from cycle to cycle.

The Automatic Elasticity Compensator circuit must use some value ofsystem elasticity. This parameter (k) is measured during the sizeinitialization step as described previously.

The Automatic Tool Protection (ATP) circuit continuously monitors theload cell any time the feed system is moving. Whether the operator ismanually moving the feed system or the feed system is automaticallysearching for the bore or the feed is running in either regulationmodes, the ATP circuit checks that the feed force stays within aspecific range. If the feed force exceeds a predetermined value then theATP circuit will immediately retract the feed system to release thegenerated force and notifies the main honing machine controller 38 tohalt all other axes.

Honing Optimization.

With this invention all pertinent feed system parameters are eithercontrolled or measured. Since the machine is computer controlled thereexists an opportunity to automatically optimize the honing performancefor the customer. Bore size control and bore cylindricity can often besatisfactorily achieved over a wide range of feed parameters. Howeverwithin this range there are trade-offs of cycle time and stone wear. Thecustomer is concerned about these inasmuch as it affects the total costper bore for the honing operation.

An optimization program included in the computer control of the machinecould request some basic information from an operator or othermanufacturing personnel regarding cost of abrasive stones, height ofabrasive stones, stones per tool, cost per hour of labor and machine,etc. Also input would be some limits to feed force and feed rate. Themachine would then run a trial for a predetermined number of workpieces.The machine would record cycle times and cumulative bore sizecompensations as a measure of stone wear. The machine could thenestimate the cost per bore under those set of feed parameters. Then thefeed force or feed rate could be varied by some predetermined incrementand another trial could be run. In this manner the machine could changeone variable (feed force or feed rate) until an optimum cost per bore isfound. At that point the trials would conclude and the machine wouldkeep its settings at the optimum values until overridden by an operator.Except for the initial query of pertinent data, all this could proceedwithout need for operator involvement or awareness.

Machine Setup.

Referring also to FIGS. 5 and 5 a, a high level flow diagram 90 of stepsof machine setup according to one method of the invention is shown.Here, it should be noted that when a new tool is installed, the controlsystem has no knowledge of the relationship between the feed systemencoder position and the diameter of the tool. An initialization step isrequired, then the following steps are preformed:

1. The operator enters setup information including the target (or final)diameter of the workpieces that will be honed, as set forth in block 92.

2. The operator measures the bore of a workpiece with some measuringdevice external to the machine, as set forth in block 94.

3. The workpiece is placed in the machine, as set forth in block 96.

4. The operator enters this measured diameter into the computer, as setforth in block 98.

5. When prompted by the operator the machine will bring the tool intothe workpiece bore and the feed system will move slowly to expand theabrasive, as set forth in block 100.

6. Before the abrasive contacts the bore the control system will samplethe load cell to determine a baseline level of force, as set forth inblock 102.

7. When the abrasive contacts the bore the force measured by the loadcell will rise. While the force is rising the control system will sampleat least two points, as set forth in block 104, a point being a datapair of encoder position and feed force. These points are referred to as(x₁, F₁), (x₂, F₂), etc, and these are used to calculate the system andtool elasticity as detailed in the mathematical description above, asset forth in block 106. The initial point, x1, corresponds to themeasured diameter of the bore. The calculated value of elasticity isstored in the computer. (As noted in the mathematical description, couldbe as simple as a single constant value (k) or it could take the form ofa more sophisticated mathematical function.)

8. One of the sampled points is chosen to be a reference point referredto as (x_(r), F_(r)) and this is stored in the computer, as set forth inblock 108.

9. The operator selects the method of feed system control: Constant orprofiled feed rate, or constant or profiled feed force. The operatorenters the values for the controlled variable chosen, as set forth inblock 110.

10. The operator may set or the machine may calculate default values forsafe limits upper of feed force and feed rate, as set forth in block112. Lower limits may also be set/calculated as indications ofinadequate honing performance.

Machine Operation—Workpiece Honing.

Referring also to FIGS. 6 and 6 a, a high level flow diagram 114including steps of a preferred method of honing a workpiece according tothe invention are shown, and are described briefly as follows.

1. The workpiece is presented to the honing tool and the machine movesthe honing tool into the bore, as denoted at block 116.

2. The feed system rapidly expands the honing element toward the bore.Immediately, while expanding, and before reaching the bore, the baselinelevel of force is determined, as denoted at block 118.

3. The feed system continues to expand rapidly until a level of force issensed that indicates that the abrasive is contacting the bore, asdenoted at block 120. During this expansion before the bore iscontacted, the feed force is sampled to determine a baseline level offorce.

4. The feed system retracts slightly to relieve the force of theabrasive against the bore, as denoted at block 122.

5. The spindle rotation and stroking motion begins, as denoted at block124.

6. The feed system rapidly returns to the point where it had contactedthe bore, as denoted at block 126.

7. The feed system then feeds the abrasive using one of the followingmethods: constant or profiled feed rate, or constant or profiled feedforce, as denoted at decision block 128 and blocks 130 and 132. If theconstant or profiled rate mode is selected, the system continuallymonitors to check if force limits have been exceeded, as denoted atblock 134. If so, the system stops the machine and outputs or displays awarning, as denoted at block 136. If the constant or profiled force modeis selected, the system continually monitors to check if rate limitshave been exceeded, as denoted at block 138. Again, if so the machine isstopped and a warning is displayed, as denoted at block 136.

8. In either instance, the system continually checks to see if thetarget encoder position (x_(t)) has been reached, as denoted at block140. If constant force is the method chosen then the target encoderposition is a static value. If any other method has been chosen, thenthe target encoder position changes dynamically as the measured forcelevel changes.

9. The system also monitors the uncontrolled variable to be sure thepreset limits are not exceeded. If they are, then the machine will stopwith a warning displayed.

10. When the target encoder position is reached the honing cycle iscomplete, as indicated at block 142.

11. The bore is measured (either by the operator or by automated gaging)and if the bore deviates from target diameter then a bore sizecorrection (usually this is for abrasive wear) is fed back to thecomputer, as denoted at block 144. This correction is used to shift thevalue of the encoder reference position, x_(r). The process is thenrepeated until the target bore size is achieved.

Thus, there has been shown and described a honing feed system havingfull control of feed, force servo stroking apparatus and system, whichovercomes many of the problems set forth above, rate and position, andmethod of operation of the same. It will be apparent, however, to thosefamiliar in the art, that many changes, variations, modifications, andother uses and applications for the subject system and method arepossible. All such changes, variations, modifications, and other usesand applications that do not depart from the spirit and scope of theinvention are deemed to be covered by the invention which is limitedonly by the claims which follow.

1. A method of honing a bore of a workpiece, comprising steps of:providing a honing tool having at least one radially expandable honingelement; providing a feed system in connection with the honing tool,including a movable feed element automatically controllably operable forapplying a feed force against the honing tool for radially expanding theat least one honing element; providing a control operable forautomatically controlling operation of the feed system; providing adevice for determining information representative of a feed forceapplied against the honing tool by the feed element and outputting asignal representative thereof to the control; providing a device fordetermining information representative of a position of the feed elementand outputting a signal representative thereof to the control;automatically operating the feed system to apply at least two levels offeed force against the honing tool when in contact with a surface of thebore to be honed and determining information representative of positionsof the feed element during the application of the feed forces,respectively; and automatically computing a value approximating anelasticity of at least the honing tool as a function of a differencebetween the two levels of feed force and the information representativeof the positions of the feed element during the application of the feedforces, and determining a value representative of a diameter of the boreduring honing thereof as a function of the value representative of theelasticity, the information representative of the feed force, and theinformation representative of the position of the feed element.
 2. Themethod of claim 1, comprising additional steps of: providing a value foran initial diameter of the bore; and determining a value representativeof an actual diameter of the bore during honing thereof as a function ofthe value representative of the elasticity, the informationrepresentative of the position of the feed element, the informationrepresentative of the feed force, and the value for the initialdiameter.
 3. The method of claim 1, comprising additional steps of:automatically operating the feed system to move the feed element toradially expand the at least one honing element unrestrained by asurface of a bore and determining information representative of abaseline feed force required for the expansion; and automaticallyoperating the feed system to move the feed element to radially expandthe at least one honing element so as to contact the surface of the boreto cause a responsive increase in the feed force to a level greater thanthe baseline feed force serving as an indicator of the contact, anddetermining a value representative of the diameter of the bore as afunction of a position of the feed element at a time of the contact. 4.The method of claim 3, wherein the step of determining informationrepresentative of a baseline feed force required for the expansioncomprises determining a range of values for the feed force.
 5. Themethod of claim 4, wherein the honing element comprises a radiallyexpandable sleeve.
 6. The method of claim 3, comprising additional stepsof: automatically honing at least two bores to a predetermined enlargeddiameter, including for each of the bores performing the step ofoperating the feed system to move the feed element to radially expandthe at least one honing element so as to contact the surface of thebore, and determining a value representative of the diameter of the boreas a function of a position of the feed element at a time of thecontact; and determining a value representative of wear of the at leastone honing element as a function of the values representative of thediameters of the bores at the contact and positions of the feed elementwhen the bores are honed to the enlarged diameter.
 7. The method ofclaim 6, comprising a further step of automatically calculating a costof honing the bores at least in part as a function of the valuerepresentative of wear.
 8. The method of claim 7, wherein the step ofautomatically calculating a cost of honing includes calculating the costadditionally as a function of a value representative of a cost ofoperating the honing machine for honing the bores.
 9. The method ofclaim 7, wherein the step of automatically honing at least two borescomprises automatically selecting different honing parameters for honingthe bores to the predetermined enlarged diameter, respectively, andhoning the bores to the enlarged diameter using the different honingparameters, and the step of automatically calculating a cost of honingthe bores includes calculating a cost for honing each of the two bores.10. The method of claim 1, comprising a further step of honing the borewhile moving the feed element at a substantially constant rate.
 11. Themethod of claim 1, comprising a further step of honing the bore with thefeed force at a substantially constant level.
 12. The method of claim 1,comprising a further step of honing the bore with the feed force varyingat levels following a predetermined profile.
 13. The method of claim 1,wherein the device for determining information representative of a feedforce applied against the honing tool by the feed element and outputtinga signal representative thereof comprises a load cell disposed betweenthe feed element and the honing tool.
 14. The method of claim 1, whereinthe device for determining information representative of a position ofthe feed element and outputting a signal representative thereofcomprises an encoder in connection with the feed element.
 15. The methodof claim 1, comprising a further step of honing the bore with a feedrate which varies at levels following a predetermined profile.
 16. Themethod of claim 1, comprising a further step of honing the bore with afeed rate which varies at levels following a profile which is determinedat least in part as a function of the information representative of thefeed force.
 17. The method of claim 1, comprising a further step ofhoning the bore with a feed force which varies at levels following aprofile which is determined at least in part as a function of theinformation representative of the feed rate.
 18. The method of claim 1,further comprising a step of providing a device automatically operablefor monitoring the information representative of a feed force andceasing honing if the feed force during honing reaches a predeterminedlevel.
 19. The method of claim 1, comprising a further step of honingthe bore while monitoring and maintaining a substantially constant loadon a spindle holding and rotating the honing tool.
 20. The method ofclaim 1, comprising a further step of honing the bore while monitoringand maintaining a load on a spindle which varies according to apredetermined profile.
 21. The method of claim 1, wherein the signalsoutputted to the control representative of the informationrepresentative of a feed force applied against the honing tool by thefeed element are conditioned as a function of a magnitude thereof.
 22. Asystem for automatically honing a bore of a workpiece to a targetdiameter, comprising: a honing tool having at least one radiallyexpandable honing element; a feed system in connection with the honingtool, including a movable feed element automatically controllablyoperable for applying a feed force against the honing tool for radiallyexpanding the at least one honing element; a control operable forautomatically controlling operation of the feed system; a device fordetermining information representative of a feed force applied againstthe honing tool by the feed element and outputting a signalrepresentative thereof to the control; a device for determininginformation representative of a position of the feed element andoutputting a signal representative thereof to the control; the controlbeing automatically operable to control the feed system to apply feedforces against the honing tool when in a restrained state and computingat least one value representative of elasticity of at least the honingtool and the feed system as a function of the applied feed forces andinformation representative of positions of the feed element during theapplication of the feed forces, and the control being automaticallyoperable for computing at least one target value for the position of thefeed element for honing the bore to the target diameter as a function ofthe at least one value representative of elasticity of at least thehoning tool, the information representative of the feed force, theinformation representative of the position of the feed element, and avalue representative of an initial diameter of the bore.
 23. The systemof claim 22, wherein the value representative of the initial diameter ofthe bore is an inputted value.
 24. The system of claim 22, wherein thecontrol is automatically operable to control the feed system to apply afeed force against the honing tool when in the bore to expand the honingelement so as to be brought into contact with a surface of the bore tocause a responsive increase in a value of the feed force indicating thecontact, and the control is automatically operable to determine thevalue representative of the initial diameter as a function of a positionof the feed element of the feed system when the contact is indicated.25. The system of claim 22, wherein the control is automaticallyoperable to control the feed system to apply a feed force against thehoning tool to cause radial expansion of the honing element thereofunrestrained by a surface of a bore and determining a valuerepresentative of a baseline feed force required for the unrestrainedexpansion, and the contact being indicated by an increase in the feedforce from the baseline feed force.
 26. The system of claim 22, whereinthe control is automatically operable for controlling the feed system tohone at least two bores to the target diameter, and for each of thebores controllably operating the feed system to move the feed element toradially expand the at least one honing element so as to contact thesurface of the bore, and determining a value representative of thediameter of the bore as a function of a position of the feed element ata time of the contact, and determining a value representative of wear ofthe at least one honing element as a function of the valuesrepresentative of the diameters of the bores at the contact andpositions of the feed element when the bores are honed to the targetdiameter.
 27. The system of claim 26, wherein the control is operable toautomatically calculate a cost of honing the bores as a function of thevalue representative of wear.
 28. The system of claim 22, wherein thecontrol is automatically operable to control the feed system to move thefeed element at a constant rate for honing the bore to the targetdiameter.
 29. The system of claim 22, wherein the control isautomatically operable to control the feed system for honing the borewith the feed force at a constant level.
 30. The system of claim 22,wherein the control is automatically operable for honing the bore withthe feed force varying at levels following a predetermined profile. 31.The system of claim 22, wherein the control is automatically operablefor honing the bore with a feed rate which varies at levels following aprofile which is determined at least in part as a function of theinformation representative of the feed force.
 32. The system of claim22, wherein the control is automatically operable for honing the borewith a feed force which varies at levels following a profile which isdetermined at least in part as a function of the informationrepresentative of the feed rate.